Add “Librarian note(s)” field to entities

### Problem

### A clear and concise description of what you want to happen

Add a “Librarian notes” field for (Librarian) editable entities.

### Expected behaviour / screenshots (ex: Figma design screenshots for UI feature)


There should be a “Librarian notes” text box too.

It would be nice if any entered “Librarian notes” would be displayed somewhat prominently on the entity page too, so fellow Librarians can easily see that there are notes for that.

### Additional Context

Sometimes a Work, Edition, or Author can have had a good deal of research put into it, but Librarians have no way to present this to other Librarians currently in a way that isn’t patron-facing. This means that hours of research etc. is either stored in a “wrong” (e.g., patron‐facing) place, only stored with the Librarian(s) who did the research, or… just gone.

Coming from *Brainz land I am used to an "Annotations" field on pretty much all entities which is for all sorts of notes (as well as edit/revision notes actually allowing for pretty lengthy and descriptive details about the sources and reasonings behind any given edit/change), so I assumed (and wrongly so!) that the `notes` field would be a good place to store such information. However, OL’s policy is much more aligned with hiding the gritty details of the librarian/metadata detective work from “regular users” (patrons), which is probably how regular libraries also operate.

### Proposal & Constraints

### What is the proposed solution / implementation?

Adding a `librarian_notes` text field in addition to existing `notes` and `description` fields, the contents of which should be shown to Librarians viewing the entity but not to regular patrons.

### Is there a precedent of this approach succeeding elsewhere?

Goodreads has such a system, though the notes are only shown when actually editing the items, not shown to GR librarians when browsing items.

### Which suggestions or requirements should be considered for how feature needs to appear or be implemented?

UI/UX considerations for how it’s shown to librarians. (This could potentially be a different issue, with this/the first issue being to just create the `librarian_notes` fields at all.)

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